Anyway, my comment is about the SSTO concept in general:
What really matters is not pure SSTO for its own sake, but an operational profile that amounts to the equivalent of SSTO.

Putting a boost-phase drop tank into the design is the simplest way to reduce vehicle mass fraction for the orbiter itself. Even if you can come close to pure SSTO function in your design, it would still make sense to use a drop tank because it gives you more margin for a robust orbiter design and for more payload.

Using an ejectable ablative nozzle insert is the simplest way to have a staged expansion ratio on the orbiter’s engines (you use an upper stage regenerative nozzle as your baseline, with the ejectable ablative nozzle inserted in it for the boost phase expansion ratio).

You don’t have to “stage” any additional engine packages, you can recover the drop tank, and the ejectable nozzle inserts are the only things you expend.

It’s unfortunate that the general public has such an irrational fear of nuclear power because I think in the long run that it’s the only way we’re ever going to do anything useful in space.

I actually proposed that they do an experiment with an Falcon 1e first stage and install an air augmented ram ejector around the engine, akin to the GNOM missile, running the Merlin a bit more fuel rich than normal. The GNOM allegedly achieved a throw weight and range equal to a standard missile twice its mass (though other than launch of a scaled version that confirmed these numbers, it remained on paper).

The F1e first stage should be SSTO ELV with almost no payload, but with a ram ejector installed should be able to put something useful in orbit.

That runs into arguments about wings on scramjets, but this is a different argument. Scramjets don’t close for two reasons that have nothing to do with the aerodynamic lift penalty – 1) They can’t start or finish the ascent, so you end up needing a separate rocket anyway; and 2) They can’t even be used to their physical limit because the Earth curves away and you lose atmosphere too quickly. An NTR does not have these problems.

The DUMBO fanboys seem blissfully unaware that the higher performance comes with a huge relaxation of fuel element containment criteria. Unlike the NERVA design, fission fragment/fuel element contamination of the exhaust was an integral feature of the DUMBO concept.

Needless to say, such a feature is (and indeed should be) a complete nonstarter today.

Good post.

The Timberwind nuclear thermal upper stage replacing the Centaur LOX/LH2 engine was supposed to have a T/W of 30; so it could work for your NTR SSTO.

I think that the only issue with posts like this is that there are thousands of assumptions that go into a rocket making it to orbit and most of these assumption have not been tested recently.

NTR SSTO actually becomes a good idea with a high T/W, but most people assume that a high T/W is impossible for nuclear thermal because they are not experts in what is possible for nuclear technology.

I would love to see a post about the high T/W particle bed nuclear thermal rockets like Timberwind which were researched in the 1980′s at a T/W over 30. Are they viable today with some funding?

I would also love to see a post on whether or not nuclear fission power in space can reach the 1 kg/kw threshold needed for 39-day voyages to Mars discussed for the VASIMR engine and also researched for Space Lasers in the 1980′s. The low-weight radiators and nuclear fission reactors for this supposedly already exist today, but most people just dismiss the entire concept of VASIMR and multi-megawatt nuclear-powered lasers because they assume that it is impossible for us to rapidly improve what has already flown in space by an order of magnitude or so (eventhough the success of the Falcon-9 has shown that you can do things different by orders of magnitude and be successful).

I would also love to see a post discussing if SSTO is possible today using the existing 3,000-lb 1st stage of the SpaceX Falcon-1e or the 33,000-lb 1st stage of the Falcon-9. Both appear to exceed the 95% propellant mass fraction needed for SSTO with LOX/RP-1.

How far is Jon Goff and Masten away from high T/W engines and structures for SSTO……probably very far, but that would also be a great post.

Your post has actually done a good job of showing why NTR SSTO is a good idea……for T/W above 20.